This invention relates to charge pump DC/DC converters. More specifically, this invention relates to charge pump DC/DC converters with reduced noise at the input voltage source.
A charge pump DC/DC converter is a power supply circuit that provides a regulated output voltage to a load from an input voltage source. One type of charge pump DC/DC converter is a switching DC/DC converter power supply that uses switches to convert the input voltage to a regulated output voltage. The switches are operated in sequence to first charge a capacitor from the input voltage and then transfer the charge to the output.
However, one of the most common drawbacks of switching power supplies is the noise induced on the input voltage source due to fluctuations or variations in the current drawn by the converter power supply. When current flows from the input voltage to the capacitor, the input voltage is loaded causing it to decrease slightly. When the capacitor is decoupled from the input voltage, the input voltage rises. These voltage changes appear as noise on the input voltage bus. The magnitude of these changes in the input voltage level depends upon the equivalent series resistance of the input voltage source and the magnitude of the changes in the input current.
Certain applications such as cellular telephones, precision instrumentation, etc. are sensitive to noise generated on the input voltage. Therefore, noise on the input voltage caused by a power supply must be filtered to prevent degraded electrical performance in other circuitry that is powered from the same input voltage source.
It would therefore be desirable to provide a charge pump DC/DC converter that has reduced noise on the input voltage source.
It would therefore be desirable to provide a charge pump DC/DC converter with a substantially constant input current.
It is an object of the present invention to provide a charge pump DC/DC converter that has reduced noise on the input voltage source.
It is an object of the present invention to provide a charge pump DC/DC converter with a substantially constant input current.
These and other objects of the present invention are provided by charge pump DC/DC converters including circuitry to reduce variations in the input current, and methods for using the same. The circuitry may include an adjustable resistor, current mirror, or current mirrors coupled to the input voltage, and feedback loop circuitry. The feedback loop circuitry is coupled to the output voltage, and responds to changes in the output voltage to control the output current of the charge pump to maintain the output voltage at the regulated value. Additional circuitry may be added to charge pumps of the present invention to provide a substantially constant input current during the blanking intervals when all of the switches are open. Charge pump DC/DC converters of the present invention include buck and boost converters.